Resistance wire or the like



Patented July 11, 1939 UNITED .STATES RESISTANCE WIRE OR THE LIKE Carl Albert Henry Jahn, London, England, assignor to Johnson Matthey & Company Limited, Hatton Garden, London County, England No Drawing. Application February 11, 1939, Serial No. 255,997. In Great Britain March 5,

3 Claims. (01. 201-76) The use of platinum and alloys of platinum with iridium in the form of line wires as electrical resistances, particularly for the ignition of explosives and in blasting caps is already well 5 known. It has already been proposed to substitute for these materials an alloy composed of 80 per cent of platinum, 15 per cent of rhodium and 5 per cent of ruthenium since this alloy has a lower specific gravity and therefore there is a greater length per unit of weight. In common with indie-platinum alloys,- the said alloy wire also has a much greater breaking strain than a wire of platinum alone.

It is an object of this invention to provide an alloy which has a still lower specific gravity combined with a greater electrical resistance so that a greater length of fine wire, for a given electrical I have found that rhodiumand ruthenium have an almost identical eiiect in reducing the specific gravity and increasing the electrical resistance of alloys of platinum and palladium.

As two examples of alloy wires in accordance with this invention I may mention the followmg:-

'(1) 70 per cent of platinum, per cent of palladium and 10 per cent of rhodium. (2) 74 per cent of platinum, 20 per cent of palladium and 6 per cent of ruthenium.

The following tablegives a comparison of the characteristics of the above two alloys with those of known alloys, all being in'the form of wire having a diameter of 0.0015 inch.

- Pt/Ir Pt/Rh/Ru Pt/Pd Rh Pt/Pd/Ru 2o 80/20 80 /15 /5 70 20 10 14 120 ,16

Breaking strain in grams 182 140-150 140-165 120 Electrical resistance in ohms per oo 85 100 100 13a Speciflc gravity 21. 57 18. 7 17.02 17. 57 Approximate length in feet per 2 ounce troy 4871 5600 6200 5900 resistance, can be obtained from a given weight of alloy.

It'is a further object of this invention to provide a fine wire eminently suitable for use as electrical resistances, for example for the ignition of explosives or .in blasting caps.

I have now found that the addition of one of the hardening metals rhodium and ruthenium to an alloy of platinum and palladium produces analloy having the desired low specific gravity, high electrical resistance and satisfactory breaking strain. Alloy wires in accordance with this invention are composed of 60 to 80 per cent of platinum, 10 to 30 per cent of palladium and from 2 to 15 per cent of one of the hardening metals rhodium and ruthenium. 'Ihese alloys have a specific gravity of less than 18, and, in the form of wire having a diameter of 0.0015 inch, an electrical resistance of at least 100 ohms per foot.

Since palladium is usually much cheaper than platinum, and since with the alloys according to this invention a greater length of wire per ounce can be obtained, the cost of a given length of wire is considerably less.

What I claim is:

1. Electrical resistance wire composed of from to 80 per cent of platinum, from 10 to 30 per cent of palladium and from 2 to 15 per cent of one of the hardening metals rhodium and ruthenium.

2. Electrical resistance wire composed of per cent of platinum, 20 per cent of palladium and 10 per cent of rhodium.

3. Electrical resistance wire composed of it per cent of platinum, 20 per cent of palladium and 6 per cent of ruthenium.

CARL ALBERT HENRY JAHN. 

